A research focus in current concrete academia is on improving the durability of the concrete and prolonging t he actual service life of the concrete. The key is to control permeability of the concrete. At present, the permeability performance of the concrete is represented by permeability coefficients of permeable media such as water, O2, N2, air and the like. According to test places, the test includes field tests and laboratory tests.
The Figg method and the Cembureau method are commonly used at present as permeability coefficient test methods which adopt gas as the permeable medium.
The Figg method can determine compactness of the concrete in a laboratory and a field environment and belongs to a semi-destructive method. During test, a pore of 10 mm is drilled in the surface of the concrete. The depth of the pore is about 40 mm. After float ash in t he pore is removed, a rubber plug tightly clinging to a wall of the pore is punched into the pore. A closed region is formed in a lower portion of the pore. Then a needle tube penetrates through the center of the rubber plug. The needle tube is externally connected with a vacuum pump with a valve. The closed region is vacuumed during test. The absolute pressure in the region is less than 0.45 MPa. The vacuum pump is turned off. Due to the leakage of concrete micropores, the vacuum degree is gradually decreased along with t he time. A measured index is the time spent when the absolute pressure in the closed region is changed from 0.45 MPa to 0.50 MPa, and the unit is second. Although equipment used in this method is simple, a sealing effect is not ideal. The reliability and reproducibility of test results are questioned by the academia.
In 1989, Kollek proposed the Cembureau method for determining the permeability coefficient of concrete by using O2 as the permeable medium, which was widely accepted internationally. A principle of the Cembureau method is as follows: a stable air pressure is applied to a test sample; and a gas flow permeating the test sample under this pressure is recorded and then converted into the permeability coefficient which is used for comparing the permeability of the concrete. The method adopts a tire-type sealing structure. The sealing effect is very good, and test steps are also very strict. But this method still can only test the test sample in the laboratory, and cannot test the gas permeability of the concrete in the field environment. However, only the impermeability of a surface portion actually determines the field concrete durability. Therefore, the test result in the laboratory cannot completely reflect the actual impermeability and durability of the concrete.
Therefore, the research objective of those skilled in the art is to study a test method which is simple in operation, good in sealing effect, easy in carrying equipment, and capable of testing the gas permeability coefficient of the concrete in the field.